As a corollary to my last post, here’s an analogy for you:

The difference between 16-bit (CD-quality) and 24-bit (“HD”) audio is 8 bits, and 2**8 = 256. That means that 24-bit audio can provide up to 256 times the amplitude “depth” of 16-bit.

Let’s compare audio bit depth with water depth. The surface of the water is analogous to unity gain, 0 dB. Unity gain is the loudest representation of sound a digital audio signal can provide. When multiple successive samples hit unity gain, the signal isn’t describing anything during that time. It’s just being loud. Severely brickwall-limited audio can have lots of samples whose value is 0dB. Think of this audio as a swimmer that stays on the water’s surface. They always swim on the top of the water, regardless of the depth.

Let’s say 16-bit audio is like a part of an ocean where there’s a 16-foot-deep coral reef. If a swimmer holds their breath, they can swim down below the surface and explore a bit, and find lots of neat stuff. There’s probably more interesting stuff under the surface of the water than at the top. When audio waveforms steer clear of unity gain (i.e. by not being clipped), more of their original resolution is present.  They can be heard more accurately, just like diving below the surface of the water helps the diver to see the objects that are under water more accurately.

Now, let’s say 24-bit audio is water that’s 256 times deeper than that 16-foot section: about 4100 feet deep; almost a mile. Again, the swimmer could stay on the surface, but they’ll be able to find much more life underneath. Putting on some scuba gear or deep-sea-diving equipment, they’ll be able to go even deeper than when they hold their breath, and potentially find lots more stuff. When audio waveforms don’t hit unity gain and can use at least some of the extra resolution that 24 bits provide vs. 16, they can be played back with even more accuracy. However, if the swimmer (in the case of recorded music, the mastering engineer) stays near the water’s surface, they won’t find much.

Mastering engineers need to learn to swim below the water’s surface before the music industry moves to 24-bit formats by default.